FIG. 1 shows an electronic circuit 100 of the prior art, which includes a power amplifier 102 coupled to a harmonic filter 104. Power amplifier 102, which includes a Wilkinson power combiner, has an amplifier 106, an amplifier 108, a resistor 110, a transmission line section 112, and a transmission line section 114 coupled as shown. Harmonic filter 104 consists of several discrete electrical components such as capacitors and inductors. When an operating signal is applied at an input 116, power amplifier 102 provides for linear amplification which results in an amplified operating signal at an output 118. Due to non-idealities of amplifiers 106 and 108, however, power amplifier 102 also generates undesirable signals such as harmonic signals at output 118. Typically, such harmonic signals can be reduced in amplifiers 106 and 108 only with a resulting undesirable tradeoff in amplifier efficiency. Capacitance and inductance values of the capacitors and inductors of harmonic filter 104 are selected to reject or filter out such harmonic signals, resulting in an amplified and filtered operating signal at an output 120.
FIG. 2 shows another circuit of the prior art, an electronic circuit 200 including a power amplifier 202 and a harmonic filter 204. Power amplifier 202, which includes a Wilkinson power combiner mentioned above, has an amplifier 206, an amplifier 208, a resistor 210, a transmission line section 212, and a transmission line section 214 coupled as shown. When an operating signal is applied at an input 216, power amplifier 202 generates an amplified operating signal and harmonic signals at an output 218. Harmonic filter 204 consists of transmission line sections and capacitors having electrical values selected to reject such harmonic signals, resulting in an amplified and filtered operating signal at an output 220.
FIG. 3 shows another circuit of the prior art, an electronic circuit 300 including a power amplifier 302 and a harmonic filter 304. Power amplifier 302, which includes a ninety-degree hybrid power combiner, has a phase shifter 305, an amplifier 306, an amplifier 308, transmission line sections 310, 312, 314, and 316, and a resistor 318 coupled as shown. When an operating signal is applied at an input 320, power amplifier 302 generates an amplified operating signal and harmonic signals at an output 322. Harmonic filter 304 consists of transmission line sections having impedances chosen to filter out harmonic signals, resulting in an amplified and filtered operating signal at an output 324. In the prior art, power amplifiers 102, 202, and 302 of FIGS. 1-3 have been used interchangeably with harmonic filters 104, 204, and 304.
Although electronic circuits 100, 200, and 300 of the prior art function as required, they include many electrical components which together consume a great deal of physical space on a substrate and allow for considerable signal loss of the operating signal. Accordingly, there is a need for power amplifier and filter circuitry that consumes less physical space and allows for less signal loss of the operating signal, and circuitry especially suitable for high-powered radio transmitters.